The present invention relates to an electronically commutated motor including a stator carrying a plurality of winding strands and a rotor in which the individual winding strands are controlled via power amplifiers in staggered periods of time, the periods being subdivided into control time and idle time.
In conventional electronically commutated motors, the motor power output is influenced by the pulsing of the power amplifiers via pulse width modulation or by variation of the limit switching time of the power amplifiers. Normally, the current is pulsed over the total time of control or varied in the limit switching time. At high motor currents, this results in high switching losses which increase roughly quadratically with the current. These high switching losses reduce the efficiency of the motor and also result in a considerable thermal load on the power amplifiers which frequently can also result in a failure of the electronic switching element used in the power amplifiers.
An object of the present invention is to improve the control of an electronically commutated motor in such a way that the high switching losses and an increased loading of the power amplifiers can be avoided at high motor currents.
According to the present invention, the object is achieved firstly in that the control times are subdivided into an initial time segment and a final time segment, that at low motor currents the power amplifiers are pulsed in the initial time segments only via pulse width modulation and that at high motor currents the power amplifiers are completely switched through additionally in the final time segments with a more or less long closing time, or secondly in that the control times are subdivided into an initial time segment and a final time segment, that at low motor currents the power amplifiers are pulsed in the final time segments via pulse width modulation and that at high motor currents the power amplifiers are switched through completely in the total final time segments and additionally in the initial time segments with a more or less long closing time.
In an embodiment according to the present invention the pulse width modulation is only carried out in the initial time segment or in the final time segment of the control time and with a pulse width that becomes greater with increasing motor current. At high motor currents, an additional closing time is added to the initial time segment or the final time segment, the additional closing time becoming greater with increasing motor current and ultimately being able to encompass the total final time segment or initial time segment. During the initial or final time segment and during the additional closing time, the power amplifier is completely switched through in order to avoid switching losses.
The two operating modes of low and high current can be separated most readily by the fact that the areas with low and high motor currents are differentiated by specification of a certain current value, the pulse width becoming greater with increasing low current and the closing time becoming greater with increasing high current.
If it is provided according to one embodiment according to the present invention that the initial time segments of the control times of the periods for the power amplifiers partially overlap and are only pulsed in the non-overlapping partial segments, then the individual winding currents do not overlap and no gap occurs in the total current if at high currents care is taken that the closing time immediately follows the initial time segment and extends more or less over the final time segment.
The control time and the idle time in the periods may be selected to be of equal length while the control time extends over approximately ⅔ of the period.
The pulse frequency for the pulse width modulation may be selected above the audible range of the human ear, e.g., 20 kHz.
The control time is increased by the fact that the closing time immediately follows the initial time segment and extends more or less over the final time segment or that the closing time extends more or less into the assigned initial time segment of the period.
The control circuit with the power amplifiers controlled in this manner can be used not only for an electronically commutated motor, but also for other loads that can also be controlled and regulated with it with correspondingly reduced switching losses and increased efficiency.